1. Field of the Invention
The present invention relates to composite materials which can be designed to have breathable barrier applications and which may be particularly useful as a component of fasteners of the hook and loop type typified by those extensively marketed by VELCRO INTERNATIONAL and now available from numerous sources for applications from shoe ties to golf gloves and many others where nonpermanent attachment is desired. These fasteners fundamentally include a hook member and a loop member that, when pressed together, entangle in a manner that resists shear forces but can be separated when subjected to a desired level of peel force. The design of these members has become quite sophisticated and provides a wide range of properties obtainable by varying factors such as hook shape, size and flexibility as well as similar loop features. For many low cost applications such as fasteners for disposable garment applications like diapers and adult incontinent wear, it has been necessary to develop inexpensive manufacturing techniques and materials for such fasteners that, nevertheless, meet the performance requirements. Particularly for such applications where the loop component also serves as the backing material, it is highly desirable that it can be breathable for comfort and also that it serve as a barrier to prevent leakage. The present invention provides a composite of film and nonwoven fabric for use as an ideal loop fastener component particularly suited to such disposable product applications.
2. Background
The art is replete with references to hook and loop type fasteners and components for such fasteners intended for use in disposable product applications such as disposable diapers and the like. Just by way of example, reference may be had to coassigned U.S. Pat. No. 5,614,281 to Jackson et al. which, itself, provides much background information and for that purpose is incorporated herein by reference in its entirety. Other loop fastener materials are described in, for example, U.S. Pat. No. 4,761,318 to Ott et al., U.S. Pat. No. 5,032,122 to Noel et al., U.S. Pat. No. 5,326,612 to Goulait, U.S. Pat. No. 5,595,567 to King et al, and U.S. Pat. No. 5,647,864 to Allen et al. Briefly, a particularly economical loop component may be formed using nonwoven manufacturing techniques such as spunbonded processes that result in significant areas of the web between bond points where the filaments are unbonded to each other and available to engage hooks of a complementary hook member. Factors, such as configuration, number and area coverage of the bonds in the nonwoven as well as the selection of a particular hook member, may be varied to achieve a desired level of peel strength and other properties within a designated cost range. In addition, the selection of a polymer or other compositional ingredient for the nonwoven and/or the hook component can affect the performance and/or cost of the fastener in a given application. There remains a need for a loop fastener component that can have tailored properties such as peel strength, shear strength and refastenability as well as barrier and, if desired, breathability functions at a cost consistent with use as a backing component of disposable products. Other uses for breathable barrier materials having clothlike attributes such as surgical gowns and drapes, for example, will be apparent to those skilled in the art.
The present invention is directed to a nonwoven and film composite material that can include properties making it particularly adapted for use as a loop fastener component that includes a laminate of a film layer and a prebonded nonwoven layer wherein the laminate bonds are separate and independent of the bond sites of the prebonded nonwoven while leaving filaments or fibers between such laminate bond sites both bonded and unbonded. For improved comfort and utility as a backing component of a personal care product such as a disposable diaper, for example, the laminate can be breathable with a moisture vapor transmission rate above about 100 g/m2/24 hours and can have a hydrohead value of at least 50 mbar. In use with a complementary hook component, a loop fastener formed from this composite provides capability for fastening anywhere on the backing of the product and consistent refastenability over a period of time and for the number of cycles of opening and closing that is suitable for many disposable and limited use applications. The nonwoven layer contains a bond pattern of either uniform or nonuniform bond impressions that result in an unbonded area of at least 70%, taken over any 100 cm square of nonwoven surface. In addition the bond frequency provides a pattern density in the range of from about 50 to about 200 bonds/in.2 with an area coverage of from about 5% to about 30%, advantageously from about 10% to about 25%. The film layer is either a multilayer or coextruded structure with an exposed layer of a soft, amorphous polymer, or a monolayer and, in either case, is a predominantly microporous barrier to liquid that is conformable and compatible with the nonwoven. Lamination may be achieved by an application of heat and pressure taking advantage of the amorphous polymer properties either in the multilayer film, or as the separately applied bonding layer in the monolayer film embodiment, for example. The independent laminate bond pattern is selected so that areas between the laminate bonds contain separate nonwoven bonds that further integrate the fibers or filaments of the nonwoven surface. For example, laminate bond patterns may have less than 50% coverage of the laminate surface area, advantageously less than about 30% and may be uniform or nonuniformly shaped and/or configured and will generally be significantly fewer in number than the nonwoven prebonds. To enhance clothlike aesthetics and engagement of hook elements for the loop component applications, a retracted laminate may be formed by stretching the film prior to lamination to the nonwoven and subsequently allowing the laminate to relax or retract, producing a pillowed/highly bulked nonwoven film laminate between bond areas where the film and nonwoven remain securely attached. The invention also includes the method for making the composite.
Definitions
As used herein the following terms have the specified meanings, unless the context demands a different meaning, or a different meaning is expressed; also, the singular generally includes the plural, and the plural generally includes the singular unless otherwise indicated.
xe2x80x9cNonwovenxe2x80x9d means a web of fibers or filaments that is formed by means other than knitting or weaving and that contains bonds between some or all of the fibers or filaments; such bonds may be formed, for example, by thermal, adhesive or mechanical means such as entanglement.
xe2x80x9cFiberxe2x80x9d means an elongated strand of defined length, such as staple fibers formed by cutting a continuous strand into lengths of, for example, 2 to 5 cm. Collections of fibers may have the same or different lengths.
xe2x80x9cFilamentxe2x80x9d means a generally continuous strand that has a very large ratio of length to diameter, for example, 1000 or more.
xe2x80x9cSpunbondxe2x80x9d means a nonwoven of filaments formed by melt extrusion of a polymer into strands that are quenched and drawn, usually by high velocity air, to strengthen the filaments which are collected on a forming surface and bonded, often by the patterned application of heat and pressure. Spunbonded processes are described, for example, in the following patents to which reference may be made for additional details: U.S. Pat. No. 4,340,563 to Appel et al., U.S. Pat. No. 3,802,817 to Matsuki et al., and U.S. Pat. No. 3,692,618 to Dorschner et al.
xe2x80x9cLoopxe2x80x9d means an area of separation of at least one fiber or filament from others in a nonwoven and includes but is not limited to configurations where the same fiber or filament intersects itself; i.e. a complete circle or oval, for example, need not be formed.
xe2x80x9cComplementary hookxe2x80x9d means a structure adapted for use as a mechanical fastener component and having projections of a profile, height, density, geometry and orientation so as to releasably attach to a loop fastener material of the invention and provide the intended level of hook peel and shear strength properties. The projections need not form a xe2x80x9chookxe2x80x9d but may have other configurations such as a mushroom shape, for example. Suitable hook materials may be unidirectional or bidirectional, for example, and often comprise from about 16 to about 620 hooks per square centimeter and hook heights of from about 0.00254 cm to about 0.19 cm. They are available, for example, from Velcro International of Manchester, N.H. and 3M of St. Paul, Minn.
xe2x80x9cAmorphous Polymerxe2x80x9d when used herein to describe a bonding layer either as a multilayer film component or separately applied layer means a thermoplastic polymer such as certain polyolefins with a density in the range of from about 0.85 to about 0.89 and low crystallinity, for example, less than about 30% such as those frequently used as components of adhesives and having limited hot melt properties.
xe2x80x9cThermal point bondingxe2x80x9d involves passing a fabric or web of fibers to be bonded between a heated calender roll and an anvil roll. The calender roll is patterned in some way so that the entire fabric is not bonded across its entire surface. As a result, many patterns for calender rolls have been developed for functional as well as aesthetic reasons. As will be understood by those skilled in the art, bond area percentages are, of necessity, described in approximations or ranges since bond pins are normally tapered and wear down over time. As those skilled in the art will also recognize, references to xe2x80x9cpins/in.2xe2x80x9d and xe2x80x9cbonds/in.2xe2x80x9d are somewhat interchangeable since the anvil pins will create bonds in the substrate in essentially the same sizes and surface relationship as the pins on the anvil. For the nonwoven, one example of a pattern has points and is the Hansen Pennings or xe2x80x9cHandPxe2x80x9d pattern with about a 30% bond area with about 200 bonds/square inch as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. The HandP pattern has square point or pin bonding areas wherein each pin may have a side dimension of 0.038 inches (0.965 mm), for example, resulting in a pattern having a bonded area of about 30%. Another typical point bonding pattern is the expanded Hansen and Pennings or xe2x80x9cEHPxe2x80x9d bond pattern which produces a bond area of about 15% to 18% which may have a square pin having a side dimension of 0.037 inches (0.94 mm), for example, and a pin density of about 100 pins/in2. Another typical point bonding pattern designated xe2x80x9c714xe2x80x9d has square pin bonding areas wherein each pin may have a side dimension of 0.023 inches, for example, for a bond area of 15% to 20% and about 270 pins/in2. Other common patterns include a xe2x80x9cRamischxe2x80x9d diamond pattern with repeating diamonds having a bond area of 8% to 14% and 52 pins/in.2 as well as a wire weave pattern looking as the name suggests, e.g. like a window screen and having a bond area of 15% to 20% and 302 pins/in.2. Typically, the percent bonding area varies widely from around 10% to around 30% of the area of the fabric laminate web and the number of pins/in2 also may vary over a wide range. Of the practically limitless combinations of bond configurations, however, only selected bond patterns are useful in accordance with the invention. These will have a bond area in the range of from about 5% to about 30%, desirably in the range of from about 10% to about 25% and a pin density in the range of from about 50 to about 200 per square inch, desirably in the range of from about 75 to about 125 per square inch. When used herein, the term xe2x80x9cprebondedxe2x80x9d nonwoven means those nonwovens having been bonded with a pattern defined as useful in accordance with these parameters. As is well known in the art, the spot bonding holds the laminate layers together as well as imparts integrity to each individual layer by bonding filaments and/or fibers within each layer.
Examples of laminate bond decorative patterns used to overbond or laminate the prebonded nonwoven to the film are C-Stars and Baby Objects as shown in FIGS. 5 and 6. The C-Star pattern has a cross-directional bar or xe2x80x9ccorduroyxe2x80x9d design interrupted by shooting stars and generally has a percent bond area of about 17% and the Baby Objects pattern (also illustrated in coassigned U.S. Design Pat. No. 356,688 to Uitenbroek et al. dated Mar. 28, 1995) has a percent bond area in the range of from about 12% to about 20%.
Test Procedures
Hydrohead: A measure of the liquid barrier properties of a fabric is the hydrohead test. The hydrohead test determines the height of water (in mbars) which the fabric will support before a predetermined amount of liquid passes through. A higher hydrohead reading indicates that a fabric is a better barrier to liquid penetration than a fabric with a lower hydrohead. The hydrohead test is performed according to Federal Test Standard 191A, Method 5514.
Grab Tensile test: The grab tensile test is a measure of breaking strength and elongation or strain of a fabric when subjected to unidirectional stress. This test is known in the art and conforms to the specifications of Method 5100 of the Federal Test Methods Standard 191A. The results are expressed in pounds or grams to break and percent stretch before breakage. Higher numbers indicate a stronger, more stretchable fabric. The term xe2x80x9cloadxe2x80x9d means the maximum load or force, expressed in units of weight, required to break or rupture the specimen in a tensile test. The term xe2x80x9ctotal energyxe2x80x9d means the total energy under a load versus elongation curve as expressed in weight-length units. The term xe2x80x9celongationxe2x80x9d means the increase in length of a specimen during a tensile test. The grab tensile test uses two clamps, each having two jaws with each jaw having a facing in contact with the sample. The clamps hold the material in the same plane, usually vertically, separated by 3 inches (76 mm) and move apart at a specified rate of extension. Values for grab tensile strength and grab elongation are obtained using a sample size of 4 inches (102 mm) by 6 inches (152 mm), with a jaw facing size of 1 inch (25 mm) by 1 inch, and a constant rate of extension of 300 mm/min. The sample is wider than the clamp jaws to give results representative of effective strength of fibers in the clamped width combined with additional strength contributed by adjacent fibers in the fabric. The specimen is clamped in, for example, a Sintech 2 tester, available from the Sintech Corporation, 1001 Sheldon Dr., Cary, N.C. 27513, an Instron Model (trademark), available from the Instron Corporation, 2500 Washington St., Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Phila., Pa. 19154. This closely simulates fabric stress conditions in actual use. Reported results are the average of three specimens tested and the test may be performed with the specimens in the cross direction (CD) or in the machine direction (MD).
Strip Tensile: The strip tensile test is similar to the grab tensile and measures the peak and breaking loads and peak and break percent elongations of a fabric. This test measures the load (strength) in grams and elongation in percent. In the strip tensile test, two damps, each having two jaws with each jaw having a facing in contact with the sample, hold the material in the same plane, usually vertically, separated by 3 inches and move apart at a specified rate of extension. Values for strip tensile strength and strip elongation are obtained using a sample size of 3 inches by 6 inches, with a jaw facing size of 1 inch high by 3 inches wide, and a constant rate of extension of 300 mm/min. The Sintech 2 tester, available from the Sintech Corporation, 1001 Sheldon Dr., Cary, N.C. 27513, the Instron Model (trademark), available from the Instron Corporation, 2500 Washington St., Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Phila., Pa. 19154 may be used for this test. Reported results are the average of three specimens tested and the test may be performed with the specimen in the cross direction (CD) or in the machine direction (MD).
Peel test: In peel or delamination testing a laminate is tested for the amount of tensile force which will pull the layers of the laminate apart. Values for peel strength are obtained using a specified width of fabric, clamp jaw width and a constant rate of extension. For samples having a film side, the film side of the specimen is covered with masking tape, or some other suitable material, in order to prevent the film from ripping apart during the test. The masking tape is on only one side of the laminate and so does not contribute to the peel strength of the sample. This test uses two clamps, each having two jaws with each jaw having a facing in contact with the sample, to hold the material in the same plane, usually vertically, separated by 2 inches to start. The sample size is 4 inches wide by as much length as necessary to delaminate enough sample length. The jaw facing size is 1 inch high by at least 4 inches wide, and the constant rate of extension is 300 mm/min. The sample is delaminated by hand a sufficient amount to allow it to be clamped into position, and the clamps move apart at the specified rate of extension to pull the laminate apart. The sample specimen is pulled apart at 180xc2x0 of separation between the two layers, and the peel strength reported is an average of three tests, peak load in grams. Measurement of the force begins when 16 mm of the laminate has been pulled apart, and it continues until a total of 170 mm has been delaminated. The Sintech 2 tester, available from the Sintech Corporation, 1001 Sheldon Dr., Cary, N.C. 27513, the Instron Model (trademark), available from the Instron Corporation, 2500 Washington St., Canton, Mass. 02021, or the Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Phila., Pa. 19154, may be used for this test. The test may be performed with the specimen in the cross direction (CD) or in the machine direction (MD).
Martindale Abrasion test: This test measures the relative resistance to abrasion of a fabric. The test results are reported on a scale of 1 to 5, with 5 being the least wear and 1 the most, after 120 cycles with a weight of 1.3 pounds per square inch. The test is carried out with a Martindale Wear and Abrasion Tester such as model no. 103 or model no. 403 available from James H. Heal and Company, Ltd. of West Yorkshire, England. The abradant used is a 36 inch by 4 inch by 0.05 inch thick silicone rubber wheel reinforced with fiber glass having a rubber surface hardness 81A Durometer, Shore A of 81 plus or minus 9. The abradant is available from Flight Insulation Inc., a distributor for Connecticut Hard Rubber, 925 Industrial Park, NE, Marietta, Ga. 30065.
Basis Weight: the basis weights of various materials described herein were determined in accordance with Federal Test Method No. 191A/5041. Sample size for the sample materials was 15.24xc3x9715.24 centimeters, and three values were obtained for each material and then averaged. The values reported below are the averages.
Hook Peel: the 180xc2x0 peel strength test is intended to measure how well hook and loop components engage and it involves attaching a hook material to a loop material of a hook and loop fastening system and then peeling the hook material from the loop material at a 180xc2x0 angle. The maximum load is recorded in grams as an average of the three highest peak load values needed to disengage or peel the two materials. To perform the test, a continuous rate of extension tensile tester with a 5000 gram full scale load is required, such as a Sintech System 2 Computer Integrated Testing System available from Sintech, Inc., having offices in Research Triangle Park, N.C. A 3 inch (7.6 cm) by 6 inch (15.2 cm) sample of the loop material is used. A 2.5 inch (6.3 cm) wide sample of hook material, which is adhesively and ultrasonically secured to a substantially inelastic, nonwoven material, is positioned hook side down over and applied to the upper surface to cover the loop material sample with about a one inch overlap. To ensure adequate and uniform engagement of the hook material to the loop material, a wringer, Model LW 1, part number 14-9969 from Atlas Electric Devices Co., Chicago, Ill. is used to squeeze the combined hook and loop materials for one cycle, with one cycle equaling a pass through the wringer using a total of 40 pounds weight. One end of the fingertab material supporting the hook material is secured within the upper jaw of the tensile tester, while the end of the loop material directed toward the upper jaw is folded downward and secured within the lower jaw of the tensile tester. The placement of the respective materials within the jaws of the tensile tester should be adjusted such that minimal slack exists in the respective materials and the gage length is 3 inches (7.6 cm) prior to activation of the tensile tester. The hook elements of the hook material are oriented in a direction generally perpendicular to the intended directions of movement of the tensile tester jaws. The tensile tester is activated at a constant rate of separation of 500 mm per minute and the peak load in grams to disengage or peel the hook material from the loop material at a 180xc2x0 angle is then recorded, based on the average of the three highest peaks.
Hook Shear the dynamic shear strength test involves engaging a hook material to a loop material of a hook and loop fastening system and then pulling the hook material across the loop material""s surface. The maximum load required to disengage the hook from the loop is measured in grams. To conduct this test, a constant rate of extension tensile tester with a 5000 gram full scale load is required, such as Sintech System 2 Computer Integrated Testing System. A 3 inch by 6 inch sample of the loop material is attached with masking tape to a flat support surface. A sample of hook material 2.5 in.xc3x970.76 in., which is adhesively and ultrasonically secured to a substantially inelastic, nonwoven material, is positioned over and applied to the upper surface of the loop material sample centered in the shorter direction and 2 inches in from the cut edge. To ensure adequate and uniform engagement of the hook material to the loop material, a wringer, Model LW 1, part number 14-9969 from Atlas Electric Devices Co., Chicago, Ill. is used to squeeze the combined hook and loop materials for one cycle, with one cycle equaling a MD (longer dimension) pass, through the wringer using a total of 40 pounds weight. One end of the nonwoven material supporting the hook material is secured within the upper jaw of the tensile tester, and the end of the loop material directed toward the lower jaw is secured within the lower jaw of the tensile tester. The placement of the respective materials within the jaws of the tensile tester should be adjusted such that minimal slack exists in the respective materials prior to activation of the tensile tester. The hook elements of the hook material are oriented in a direction generally perpendicular to the intended directions of movement of the tensile tester jaws. The tensile tester is activated at a gage length of 3 inches and crosshead speed of 250 mm per minute and the peak load in grams to disengage the hook material from the loop material is then recorded in grams as the average of the highest peaks for three specimens.